The increased data capacity handled by computer systems has brought about an increase in the number of users who own a plurality of real storage apparatuses, and a reduction in storage running cost is wished for. Patent Literature 1 discloses a method with which a plurality of real storage apparatuses can be managed as a virtual storage apparatus. This method virtualizes numbers assigned to resources of real storage apparatuses such as volumes, pairs, and groups so that an administrator sees those numbers as resources of a virtual storage apparatus.